Adeno-associated virus (AAV) is a non-pathogenic human DNA virus that can be propagated either as a lytic virus or as a provirus. For lytic growth AAV requires the presence of a helper virus (either adenovirus or herpes simplex virus). In the absence of the helper virus, AAV readily produces cells in which one or more copies of AAV DNA are carried in the proviral form. If a latently infected cell line is superinfected with the helper, the proviral sequences are efficiently rescued and proceed through a normal AAV lytic cycle. These properties of AAV make it potentially useful both as a transducing vector for mammalian cells and also as a model for studying the biology of latent viral infections. In our previous work, we demonstrated that AAV sequences which have been cloned into a prokaryotic vector (pBR322) can be rescued from the recombinant plasmid in vivo in a fashion similar to the rescue of AAV proviral sequences from host chromosomes. We have used this infectious AAV plasmid to study the genetics of AAV as well as to construct AAV derived vectors. In this study, we propose to continue this work and also to study the mechanism of AAV DNA integration.